1. Field of the Invention
This invention relates to an exhaust system for a personal watercraft and more particularly to a catalytic exhaust system for such watercraft.
2. Description of Related Art
Personal watercrafts have become very popular in recent years. This type of watercraft is quite sporting in nature and carries a rider and possibly one or two passengers. A relatively small hull of the personal watercraft commonly defines a riders' area above an engine compartment. A two-cycle internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull that forms a front gullet portion of the tunnel.
An exhaust system of the personal watercraft discharges engine exhaust to the atmosphere either through or close to the body of water in which the watercraft is operating. Although submerged discharge of engine exhaust silences exhaust noise, environmental concerns arise. These concerns are particularly acute in connection with two-cycle engines because engine exhaust from two-cycle engines often contains lubricants and other hydrocarbons.
Such environmental concerns have raised a desire to reduce exhaustion of hydrocarbons and other exhaust byproducts (e.g., carbon monoxide and oxides of nitrogen) and thus reduce pollution of the atmosphere and the body of water in which the watercraft is operated. In response to the increased concerns regarding exhaust emissions, some personal watercraft recently have become equipped with a catalyst to convert exhaust byproducts to harmless gases.
The sporting nature of a personal watercraft subjects the catalyst to damage, however. Catalysts must operate at a relatively high temperature in order to produce the necessary thermal reaction and burning of exhaust byproducts. The sporting nature of the personal watercraft makes it likely that water occasionally will enter the exhaust system watercraft, especially if the watercraft becomes inverted and is subsequently righted. If a significant amount of water comes in contact with the catalyst, the catalyst bed can become polluted, particularly when operating in marine environments, and can even shatter.